1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer and, more particularly, to an image forming apparatus having a process cartridge detachably mounted onto the apparatus main body.
The "process cartridge" means a cartridge having a charging means, a developing means, a cleaning means, and an electrophotographic sensitive member (image bearing member), which are integrated and detachably mounted onto the image forming apparatus main body. Alternatively, at least one of the charging means, the developing means, and the cleaning means is integrated with the electrophotographic sensitive member into a cartridge detachably mounted onto an electrophotographic image forming apparatus main body. Alternatively, at least the developing means and the electrophotographic sensitive member are integrated into a cartridge detachably mounted onto the electrophotographic image forming apparatus main body.
2. Related Background Art
For a conventional image forming apparatus using an electrophotographic image forming process, a process cartridge system is employed such that an electrophotographic sensitive member and a process means acting on the electrophotographic sensitive member are integrated into a cartridge detachably mounted onto the image forming apparatus main body. According to this process cartridge system, when the developing agent or photosensitive member is consumed, the user can perform maintenance of the apparatus, e.g., replenish the photosensitive member with the developing agent or exchange it by himself/herself without requiring help of a serviceman, so that the operability can be largely improved. For this reason, the process cartridge system is popularly used for image forming apparatuses.
Some process cartridges have additional functions. For example, as disclosed in Japanese Patent Application Laid-Open No. 59-61854, a nonvolatile memory (RAM) as a memory medium is mounted in the process cartridge. The amount consumed in the image forming apparatus main body is stored in the nonvolatile RAM, and the use limit of the process cartridge is determined on the basis of the stored information, thereby prompting the user to exchange the cartridge. Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 6-149051, a quality code is stored in the above-described nonvolatile RAM at the time of delivery. Unless the quality code coincides with that of the image forming apparatus main body, the image forming operation is disabled, thus assuring apparatus protection.
The conventional process cartridge having the nonvolatile RAM uses a circuit as shown in FIG. 13 to diagnose the nonvolatile RAM, i.e., check whether the nonvolatile RAM itself normally functions, by a so-called check sum method according to the procedure shown in FIG. 14, thereby increasing the reliability.
More specifically, in the conventional image forming apparatus, when a process cartridge 20 is mounted onto an image forming apparatus main body 100 (step 1), a nonvolatile RAM 22 mounted in the process cartridge 20 and a CPU 24 mounted in the image forming apparatus main body 100 are connected through connectors 21 (21A and 21B), and a unique signal (Hi-Low signal) represented by ON/OFF of a predetermined voltage value is sent from the CPU 24 (step 2). The nonvolatile RAM 22 outputs a predetermined signal which is quantitatively converted according to the received signal to the CPU 24. Signal input to the nonvolatile RAM 22 is repeated a plurality of number of times while changing the signal contents. The CPU 24 calculates the sum of output signals.
The CPU 24 reads out an output value stored in a ROM 25 in the image forming apparatus main body in advance in correspondence with each signal output to the nonvolatile RAM 22, and calculates the sum of output values. The CPU 24 compares the sum of outputs from the nonvolatile RAM 22 with the sum of output values read out from the ROM 25 in the image forming apparatus main body 100. If the sums are equal, it is determined that the nonvolatile RAM 22 is normal, and the image forming operation starts (steps 3 and 4).
For the conventional image forming apparatus, the connectors 21 (21A and 21B) are used to connect the image forming apparatus main body 100 to the nonvolatile RAM 22 mounted in the process cartridge 20 such that the process cartridge 20 can be detachably mounted onto the image forming apparatus main body 100. Generally, the connectors 21 are constituted such that the process cartridge 20 is mounted onto the image forming apparatus main body 100 and simultaneously connected to the image forming apparatus main body 100.
When the image forming apparatus is constituted such that, when the process cartridge 20 is mounted onto the image forming apparatus main body 100, the state information of the process cartridge is read out from the memory medium such as a nonvolatile RAM and used for the subsequent image forming operation or apparatus protection, it is important to complete the read operation simultaneously at the time of mounting the process cartridge.
As described above in the related background art, generally, the memory medium such as the nonvolatile RAM 22 mounted in the process cartridge 20 and the image forming apparatus main body 100 are often connected through the connectors 21. The connectors 21 are set such that the process cartridge 20 can be easily connected to the image forming apparatus main body 100 in mounting the process cartridge 20 onto the image forming apparatus main body 100. To increase the reliability of connection, the connectors must have precise accessory components or a shape for facilitating connection.
In an image forming apparatus which communicates with the memory medium 22 mounted in the process cartridge 20 to detect the presence/absence of the process cartridge 20, if a connection failure occurs at the connectors 21, it is erroneously determined that the process cartridge 20 is not mounted even when the process cartridge 20 is properly mounted.
In the image forming apparatus which detects the abnormality of the memory medium 22 itself, when a connection failure occurs at the connectors 21, the memory medium abnormality is erroneously detected although the memory medium itself has no abnormality. In this case, the image forming apparatus performs various control operations on the basis of the erroneous detection result. For this reason, the stability of the operation of the apparatus degrades to lower its reliability.